Torque measurement



J1me 1947. H. P. KUEHNI TORQUE- MEASUREMENT Filed July 2, 1945 2Sheets-Sheet IL m 1Q o n u n ,o t vpWt n A apw June3, 1947. 1 RRKU I2,421,626

TORQ EEEEEEEEEE NT 2 Filed July 2, 1945 2' Sheets-$heet 2 His Attor ne'y.

Patented June 3, 1947 TORQUE MEASUREMENT Hans P. Kuehni, Schenectady, N.Y., assignor to General Electric Company, a corporation of New YorkApplication July 2, 1945, Serial No. 602,734

6 Claims.

such as differential variable "reactances secured to the shaft andconnect the movable element thereof to axially spaced parts of the shaftthrough small diameter flexible wires stretched taut, such that a twistin the shaft will act diiferentially on the movable element of themeasuring device to provide an amplified measurement of such twist. Inthis way the bulk, weight, size, and cost of the measuring equipmentdirectly associated with the shaft are reduced to a minimum, and due tothe differential arrangement variations in temperature, voltage,resiliency of the wires, centrifugal force, etc. cancel out and do notinfluence the measurement. Torque may be measured of shafts either inrotation or while stationary, and hence, the invention may be used formeasuring strain or relative displacement of stationary parts.

The features of my inventioriv'vhich are believed' to be novel andpatentable will be pointed out in the claims appended hereto. For abetter understanding of my invention, reference is made in the followingdescription "to the accompanyingdrawings in which Fig. 1 representssomewhat diagrammatically a plan view of a preferred embodiment of myinvention as applied for measuring the torque of a shaft; Fig. 2 is ashaft endview of the shaft apparatus of Fig. 1; Fig. 3 represents aseries parallel measurement connection that may be employed with fourmeasuring elements; Fig. 4 represents a side view of one pair of thevariable reactance elements; Fig. 5 a top view of such pair in a centralor zero measurement condition; and Fig. 6 a similar view but with thearmatures moved from a zero measurement positiOniFigs. '7 and 8represent different ways of securing parts of my measuring apparatus toa rotating shaft, and Fig. 9 an adjustable dovetail arrangement that maybe employed in the reactance measuring head.

Referring now to Figs. 1 and 2, I represents a section of a shaft thetorque of which it is desired to measure. Secured to the shaft is asupport plate 2 having a 'T-shaped radial extension 3 which ispreferably arranged to be adjustable with respect to the base plate 2.The T-shaped part 3 carries,-in this case, four variable reactancedevices 4, 5, 8 and 1 arranged in pairs at each end, these devices eachconsisting of a magnetic circuit including at least one air gap, awinding on the magnetic circuit all arranged to vary the reactiveimpedance by varying of the air gap as best shown in Figs. 4, 5 and 6.As illustratedin Figs. 4 and 5, reactance devices 4 and 6 comprise apair at one end of the T-shaped member 3, the reference numerals 4 and 6indicating the coils of such variable reactance devices. Such devicesmay comprise a U-shaped laminated magnetic ccreB secured in fixedrelation to the supporting head 3 as by parts 9 and movable magneticarmature parts I ll spaced from the parts 8 by small air gaps at H andI2, II designating the gaps for reactance device 4, and i2 the gaps forreactance device 6. The armature parts for the pair of reactance devicesare secured together in spaced relation at the end of a relatively shortand stifi resilient tongue memberl3' extruding from the end of head 3.The other reactance elements 5 and 7 comprise another similar pairsimilarly mounted at the other end of head 3.

When the armatures are in a central or zero measurement position asrepresented in Fig. 5, all of the reactance devices have equalreactance, and this occurs when the resilient tongue members arestraight as indicated in Fig. '5. It will now be seen that if the tongueI 3 be bent as represented, to an exaggerated extent, in Fig. 6, such,as might be caused by an unequal tension on wires I4 and I6 secured tothe movable armature assembly, the air gaps ll of reactance 4 willincrease while the air gaps l2 of reactance device 6 will decrease, thuschanging the pair of reactances differentially. Thus, for the conditionrepresented, the reactance of 4 will decrease and the reactance of Bwill increase. In order thus to varythe reactance in response to thetwist of the shaft, the wires It and it have their opposite ends securedto the shaft at points which are axially and circumferentially displacedfrom the head 3 as represented in Figs. 1 and 2, so that if a twistoccurs in the shaft, one wire of a pair will be tensioned and the otherwire detensioned by an amount proportional to such twist. The controlwires for the other pair of reactance devices 5 and l are indicated at15 and H in Fig. 1. Itis seen that the wires l4 and I6 extend axiallyalong the shaft by an equal amount in the same direction from head 3,but circumferentially these wires extend about the shaft an equaldistance in opposite directions. Hence, if there is a twist in the shaftbetween the axial points of support of the wires, such, for example, asrepresented by the relative direction of the arrows l8, Fig. 1, Wires l5and 15 will be tensioned and wires I4 and I! will be detensioned. Suchdirection of shaft twist will cause the direction of armature movementrepresented in Fig. 6 for that particular pair.

The anchor supports for the wires of a pair determine the base of atriangle with the gauge 7 head at its apex and these anchor pointspreferably rise above the surface of the shaft a sufiicient distancethat the wires clear the shaft as indicated in Fig. 2, although this isnot of great importance, since the tension in the wires is large ascompared to the small friction which would be encountered by contactwith the shaft. Such anchor supports may be of the character represented at l9 in Figs. 1 and 2, the supports being secured to the shaftin any suitable manner. In Figs. 1 and 2 it will be assumed that theanchors I9 and the base support 2 for the variable reactance assemblyare secured to the shaft I by a small amount of spot welding. Forinitially adjusting the tension of the wires, the ends which are securedto anchors I9 are preferably secured to a bolt 28 which may be adjustedthrough the support 19 to adjust the wire tension and then secured inplace for such adjustment. For the Wires themselves I may use piano wireor small wires'of any material having good strength and a small amountof stretch. A material such as phosphor bronzewhich does not corrodeeasily may be used. In the claims I have designated the character ofsuch wires by the expression in the nature of piano wires.

While different ways of initial calibration may be used, it will beassumed that with no torque or twist on the shaft, all four wires willbe adjusted to have the same tension with the resilient tongue membersl3 in their central positions, and with the air gaps of the severalreactance devices equal. It should be mentioned here that the wires l4and 16 should have equal tension, also wires l5 and I1, but that it isnot important tohave wires it and I5 or is and ll of equal tension ifthe head is of good rigidity and well anchored to the shaft.

In order to obtain measurements of the variation in reactance, thereactance coils are connected through slip rings and brushes to suitablestationary measuring apparatus. In Fig. 1 one side of each coil isconnected in common to a slip ring 2i and the other sides of coils 6, 1,4 and 5 are connected respectively to slip rings 22, 23, 24 and 25.Brushes 26 bear on the several slip rings and are connected to acorresponding number of measurement terminals 21.

Owing to the manner in which the measurement elements are useddifferentially in pairs, a bridge measurement circuit is appropriate,and several forms of bridge measurement circuits may be used. The oneillustrated in Fig. 1 is of the rectifier type essentially like that ofFig. 4 of United States Patent No. 1,964,141, June 26, 1934, to Rhodeset al., shown connected through slip rings 2|, 23 and 25 to reactancecoils 5 and l and a source of alternating current'supply 28. A frequencysupply of 2000 cycles will give good results. Coils 5 and I constitutetwo arms of the bridge and condensers. 29 constitute the other two armsof the bridge. A sensitive direct current measuring instrument 39 isconnected across the bridge, and a variable impedance 3i may be providedat one terminal of the bridge for final bridge balancing purposes. Forsimultaneous check readings two such rectifier instruments may be used.

If the bridge is balanced with no torque on shaft i and with equaltension on wires IQ and 55, any twist in the shaft will be indicated bya reading one instrument 3e, and the deflection from zero will beproportional to such twist or torque and the apparatus calibratedaccordingly. Then the instrument may be switched to slip rings 22 and 24to obtain a check reading using reactance coils 4 and 6. Likewise,coils. e and 5 or coils 6 and .1 may be used in pairs for check reading.Hence, four check measurements or readings are possible, and anymeasurement that appears to be badly off may be eliminated and theremainder averaged.

The apparatus may also be calibrated for dou bling the range over whichthe shaft 1 twists for a given installation as. follows: With no twistof the shaft deflect the movable armature elements it] from the centralor equal air gap positions by a readjustment of the tension in the wiresi l, i5, 56 and H in the direction opposite to that in which they willdeflect when torque is put on the shaft and balance the bridge circuitfor this condition. Then when the shaft is twisted, the instrument willread in proportion to the twist and resulting unbalance, and theapparatus may be calibrated for use in this Way. Likewise, a zero centerdirect current instrument may be used and the bridge balanced for anintermediate value of torque. It is evident that torque measurements maybe made by apparatus provided with only one pair of. the variableimpedance elements or, in fact, with only'one variable impedance on theshaft. 7 In Fig. 1, I have shown a standard impedance 32 with which theseveral variable impedances l, 5, 6 and 1 may h e-individually comparedand by means of which four additional torque measurements may be madeusing the variabl impedances individually with the standard, impedance32. The sensitivity of the measurement may be increased and averaged fora given amount of shaft twist by connecting impedances 4 and l in seriesin one arm of the bridge and connecting impedances 5: and 6 in series inthe other arm of the bridge as represented in Fig, 3. Here only threeslip rings are needed if the series connections are made between thecoils at the gauge head. The apparatus is sufficiently sensitive thatonly a comparatively short length of shaft need be used to accommodatethe installation. For example, let it be assumed that shaft I is a16-inch diameter shaft of suitable material for shaft purposes. Such ashaft whenfully loaded to safe limits'will'twist by about 0.0108 inchmeasured at'its periphery over 20 inches of shaft length. Assuming thatthe distance between the center .of the gauge head at 2 andthe anchorsat H! is 15 inches measured along the shaft, this will allow for anairfgap variation at the gauges of about 0.005 inch between zero andfull load torque, whicheXperience has shown to give a satisfactoryreactance-variation and measurement range with the type ofcircuit'proposed. The over-all shaftjlength used including that requiredfor the five 'slip rings for a 16-inch diameter shaft need not exceed 40inches for the apparatus as arranged-in Fig. 1.

It is to be noted that the apparatus will measure torque whether theshaft be rotating orstationary, and, hence, could be used for measuringrelative displacement of ports; for--.various purposes. For'instance,with the shaft stationary one could measure the direction and extentofbending. Since the measurement elements are used. difierentially in.similar pairs, temperature variations, vibration, centrifugal force,voltage variations, end play ofthe shaft, speed of rotaition,.andthelike, if they have any influence, will influence each pair of similarmeasurement ele- :ments alike and not influence the accuracy of theLmeasurement. Bending of the shaft will not in- .iiuence the measurementwhere units 6 and I or 41211115 are used in pairs. The apparatus isrelatively light in Weight, of small bulk, and easily shipped, assembledand disassembled, and compares very favorably with prior shaft torquemeasuring apparatus of like accuracy in these respects.

The parts may be secured in place on the shaft in various ways. In someinstances it will be possible to anchor the wire ends to parts alreadyon the shaft, such as couplings, etc., as indicated at I:9a in Fig. 7.The parts may also be strapped ion the shaft with steel bands 32 asrepresented in Fig. 8.

In Fig. 8 the gauge head base 2 is provided withknife edges 33 whichseat themselves on the shaft I. and when the steel band 32 is tightened,by means of tightening bolts 34 arranged to expand the band 32 withrespect to the shaft, the knife edges slightly out into the shaft. Thisseating operation may be aided by lightly tapping the head 2 with ahammer, the blows being directed toward the shaft, while the strap 32 isbeing tightened. This and other 'ways of firmly securing the gauge headand wire anchors to the shaft to prevent slippage in use and withoutinjuring the shaft may be employed. As shown in Figs. 8 and 9 the base 2is connected to the head part 3 by a. dovetailed joint at 35. By usingwedges 36 in the dovetailed joint and tightening screws 31, a rigid yetadjustable fastening together of these parts is provided.

One of the common troubles encountered with torque measuring devices isthe slipping of some part during operation due to vibration, twist ofthe shaft, etc. My torque measuring apparatus is designed to avoid suchdifficulties but should they occur during test, slippage may readily bedetected because of the several variable impedance measuring circuitsemployed and by means of which they may be checked against each other atany stage of the testing procedure. Also, after the test has beenfinished, each measuring circuit combination may be checked to see if ithas its initial calibration, and in any circuit combination which showsa serious departure from initial calibration the test reading obtainedfrom that circuit may be disregarded.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. Apparatus for measuring relative displacement at the surface of abody along a given axis comprising a pair of variable reactance devicesadapted to be secured to the surface of such body at a given point,anchors also adapted to be secured to the surface of said body at otherpoints on its surface such that said other points are at the extremitiesof the base of a triangle which is parallel to said given axis and withthe variable reactance devices located at the apex of the triangle, saidreactance devices each having a magnetic circuit containing an air gap,resilient means common to both reactance devices for determining saidair gaps and movable under force along said given axis so that as oneair gap is increased the other air gap is decreasedand vice versa andwires in .the nature of piano wires stretched between said two anchorsand theresilient air gap determining means of. said reactancestending tobias said resilient means: in opposite directions along said given axis,and a measuring circuit responsive to the differential variation of saidreactances.

.2. Equipmentfor use inmeasuring the twist of a longitudinal body suchas a shaft comprising a pair of measuring devices adapted to be anchoredto such body at a given point on its surface, said measuring deviceseach having a movable member and means responsive to the movement ofsaid member for producing an electrical response, the movable members ofsaid measuring devices being mounted on a common resilient supportmovable under pressure so as to move said members to vary the electricalresponsesof said measuring devices differentially, a pair of anchormeans adapted to be secured to the surface of such body at pointsdisplaced in the same direction along the axis of said body anddisplaced in opposite peripheral directions of said body from said pairof measuring devices, and wires in the nature of piano wires stretchedbetween said anchor means and the resilient support of said measuringdevices whereby when said body is twisted there is a differentialelectrical response of said measuring devices proportional to suchtwist.

3. Equipment responsive to the twist of a longitudinal body such as ashaft comprising a pair of electrical displacement response devicesadapted to be fixed to such body at a given point on its surface, saiddevices each having a movable member for varying the electrical responsethereof, said members being fixed to a common flexible support, subjectto displacement in response to a force, for moving said movable membersto produce a differential response in the pair of electrical devices, apair of anchor means adapted to be fixed to the surface of said body atpoints equally distant and in the same longitudinal direction from andequally distant from and in opposite peripheral directions from saidpair of displacement response devices, wires in the nature of pianowires stretched between said anchors and said flexible support such thatif there is twist in such body there will be a differential electricalresponse in the pair of electrical devices proportional to such twist,and an electrical measuring circuit for measuring the magnitude of suchdifferential electrical response.

4. Apparatus for measuring twist in shafts and the like comprising agauge head adapted to be fixed to the periphery of such shaft, fourelectrical gauging devices on said head each having a movable elementfor varying its electrical response, said movable elements being groupedin pairs and each pair being mounted on a resilient member which ismovable, laterally of the shaft, in response to pressure todifferentially vary the electrical response of the pair of gaugingdevices with which associated, four anchor elements adapted to be fixedto the periphery of said shaft at four points spaced peripherally andaxially away from said gauge head such that the gauge head liessymmetrically within the center of the anchor grouping, wires in thenature of piano wire stretched between said anchor elements and. theresilient movable elements on said gauge head, the wires to one of saidmovable elements being connected to the anchors which are spaced fromsaid gauge head in one axial direction of the shaft and the other ofsaid movable elements being connected to the anchors which are spacedfrom the gauge head in the opposite axial direction of such shaft,whereby when there is a twist in the shaft between the anchor parts,each pair of electrical gauging devices responds difierentially, anelectrical measuring circuit and connections whereby different pairs ofsaid gauging devices may be connected in said circuit for producing ameasurement proportional to the twist in such shaft.

5. In apparatus for measuring the twist of shafts, a gauge head adaptedto be temporarily but securely fixed to the surface of a circular shaftwithout injury to the shaft, said gauge head having a base with parallelknife edge ridges adapted to be set on the shaft with the ridges againstthe shaft and parallel thereto, a metal strap with its ends secured tothe sides of said base adapted to surround the shaft to strap the basethereto, a plurality of bolts threaded through the strap at differentpoints about the shaft to contact the surface of the shaft and whentightened to force the strap away from the shaft at such points therebyto tighten the strap, and gauging means adjustably secured on said baseby a dovetail connection.

6. In apparatus for measuring the twist of shafts, a gauge head and ananchor both adapted to be secured to the surface of a shaft at pointsspaced axially and peripherally of such shaft, and a fine metal wireless than inchin diameter stretched between said gauge head'and anchoradapted to be tensioned to operate the gauge in response to twist insaid shaft, said wire being secured to said anchor and gauge head partsa sufiicient distance from the surface of the shaft that it does notcontact the shaft between its ends, and means at one end of such wire atthe point where it is fastenedtfor adjusting its tension independentlyof twist in said shaft.

HANS P. KUEHNI.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS I Date Certificate of Correction Patent No.2,421,626. June 3, 1947. HANS P. KUEHNI It is hereby certified thaterror appears in the printed specification of the above numbered patentrequiring correction as follows: Column 4, line 75, for the Word portsread parts; and that the said Letters Patent should be read with thiscorrection therein that the same may conform to the record of the casein the Patent Office.

Signed and sealed this 19th day of August, A. D. 1947.

LESLIE FRAZER,

First Assistant C'ommz'ssz'oner of Patents.

